The paper bags or sacks composed of various sheets or layers are formed from rolls of paper, or sometimes from plastic materials, in two principal stages: a first stage of formation of a tubular surface open at its outer walls and a second stage of formation of the bottoms, therefore, the sack or bag.
In the first stage, points of glue are applied on the edges of the sheets. This gluing is necessary to keep the sheets together, constituting the bag or sack, during the operations of folding and gluing the bottoms.
The gluing is applied on the longitudinal edges of the sheets in order to create a closed tubular surface.
In the second phase, the formation of the bottom of the bags is obtained by folding and gluing the clearly defined flaps on the outside of the tubular surface.
In gluing the bottoms of the bags, first fold the edges of the tube to define the flaps, of which one flap has glue applied. Next, fold again on the flaps in such a way that they remain superimposed and stuck to each other. It is usual to apply a glued strip of paper on the flaps, which acts as a strengthener.
In order to produce the folds necessary for the shaping of the bottom, suction pads are used to lift up the tube, resulting in the separate sheets to be joined together by the glue. These points of gluing are the ones mentioned initially, as the process of the shaping of the bags is applied.
Transfer rollers are used, to conduct the adhesive to a roller applicator which has on its surface a plate or special band of rubber or a similar rough surface, containing small cells in which the glue is deposited and transferred to the flaps of the paper sheets for their closure, shaping the bottom of the bags.
When large quantities of the flaps for the bags are glued, you have to increase the speed of rotation of the roller applicator but, due to the morphology of the surface of the plate, may lose some of the glue due to the increase in speed.
In order for the gluing points to keep the sheets of paper together, the gluing machines have roller applicators with ruler guides to correctly set the glue points to apply the glue in the front and back openings of the different layers and sheets.
The gluing points are of rubber, plastic or metal and generally present a circular, elliptical or rectangular configuration.
These gluing points can either form part of the ruler guide or constitute independent pieces which are connected to the ruler guides by a support equipped with a lower shaft which is threaded around the said power strip and an upper shaft which is threaded around the glue point.
The configurations described above present an inconvenience when the glue accumulates on the walls of the glue point and the un-transferred glue comes off during the turning of the roller, producing unwanted spattering. On other occasions, the glue dries around the gluing points, gradually increasing the transfer surface, producing an unnecessary expense and increasing the humidity in the bag.